Rigidized printing screen

ABSTRACT

An improved process for rigidized screen for printing and the like in which the frame is zincated prior to rigidizing the screen by encapsulating the screen in nickel.

Umted States Patent 1191 1111 3,749,010 Mentone [4 1 July 31, 1973 IRlGlDlZED PRINTING SCREEN 3,482,300 12/1969 Reinke 29/160 2,891,3096/1959 Fenster 204/38 B X [751 Paul 3,202,529 8/1965 Dunlap et 81....204/38 B 73 Assignee; Buckbee Mears Company Paul 1,934,643 11/1933Rafton 245/8 Minn. 3,169,475 2/1965 Caovette 101/127.1 3,532,609 10/1970Miyata et a1. 204/38 B [22] Filed: Nov. 12, 1971 [21] Appl. No.: 198,396Primary Examiner-Robert E. Pulfrey Assistant Examiner-E. M. Coven A t Ml. 52 Us. c1. 101/127, 204/38 B, 245/8 tome) jacqbm at a [51] Int. ClB4111 1/24 [58] Field of Search 101/127, 127.1, 128.2, [57] ABSTRACT117/355; 204/33, 29, 38 B An improved process for rrgldrzed screen forprlntmg and the like in which the frame is zincated prior to ri- [56]References Cited gidizing the screen by encapsulating the screen inUNITED STATES PATENTS 2/1960 Scheeler 101/1271 nickel.

1 Claim, No Drawings I RIGIDIZED PRINTING SCREEN BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates generally toprinting screens and methods of making printing screens and, moreparticularly, to rigidized self-supporting printing screens.

2. Description of the Prior Art There are numerous printing screens andmethods of rigidizing flexible printing screens as evidenced by theRafton U.S. Pat. No. l.934,643, and the Reinke U.S. Pat. No. 3,482,300.Basically, these patents teach the coating of a screen to rigidize it byelectrolytically coating the screen with a suitable material. Forexample, the Reinke patent shows a screen which is rigidized byelectrolytically depositing nickel on a stainless steel screen. Reinkeindicates that a uniform deposit of onefourth to 1 mil of nickel on bothfaces of the screen is sufficient to rigidize the screen. While priorart processes of this type work relatively well, with screens havingstainless steel frames, they are not suitable for all applications. Forexample, problems occur when it is desired to use a lightweight framesuch as aluminum to support a screen to be rigidized. While other framessuch as stainless steel are suitable, it is oftentimes preferred to usean aluminum frame for various reasons. Generally, the aluminum frame hasgood strength, good dimensional stability, good corrosion resistancebesides being light, easy to cast, and generally less expensive thanother types of frames. The use of an aluminum frame to support a screento be encapsulated in nickel creates a problem because the aluminum isnot passive in the nickel plating solution. Consequently, to platenickel onto a screen with an aluminum frame produces a secondaryreaction in the nickel plating solution that affects the encapsulatingproperties of the nickel. Although other encapsulating materials havebeen tried, it is preferred to use a final nickel finish on the screenbecause of its strength and corrosion resistance. Furthermore, analternate method of using two plating materials, i.e., a first platingsolution to plate onto both the aluminum and stainless steel and asecond nickel plating solution to encapsulate the screen, is undesirablebecause the two layers of plating would substantially reduce theopenings in the screen.

The present invention eliminates the problem of plating on an activemetal frame such as aluminum by using two plating solutions, a firstzincating solution to plate onto the aluminum frame but not onto thestainless steel screen and a second nickel plating solution toencapsulate and rigidize the screen.

SUMMARY OF THE INVENTION Briefly, the invention comprises a process anda method for producing an improved rigidized screen with an aluminumframe for use in the printing industry. In its further embodiment theinvention includes an improved apparatus or screen for use in theprinting industry.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the preferred embodiment ofmy invention, one prepares an aluminum frame with a stainless steelscreen for rigidizing by first cleaning the screen and frame. In thefirst step, one generally cleans the aluminum frame with a stainlesssteel screen in an aluminum etch cleaner. Next, the frame and screen aresubjected to a spray rinse to remove any impurities or particles on thescreen and frame. The screen and frame are then immersed in a nitricacid bath for approximately 30 seconds to remove any remainingimpurities on the screen and frame. After the nitric acid bath, thescreen and frame are subjected to a rinse of normal tap water to removeany nitric acid and thus prepare the frame and screen for the zincationstep.

In the zincation step, the screen and frame are zincated for one minutein a zincating solution by immersing the aluminum frame and screen inthe zincating solution which typically comprises sodium hydroxide andzinc hydroxide. Although sodium hydroxide and zinc hydroxide aredescribed, other zincating solutions could also be used. During thezincating process, the outer layer of aluminum oxide is dissolved andreplaced with a fine layer of zinc while the stainless steel screenremains unaffected by the zincating solution, i.e., the zinc does notplate onto the stainless steel. Care must be taken in zincating thealuminum frame to ensure that enough zinc is plated onto the aluminumframe to cover all the exposed areas of the frame. However, too longexposure to the zincating solutin causes the zinc to form flakes andridges that fall off when the aluminum frame is immersed in the nickelplating solution. Typically, I have found for a zincating solution atroom temperature about one minute is sufficient time to produce a zinccoating of proper thickness.

After zincating, the screen and frame are removed and washed with adeionized water spray to remove any zincating solution on the frame andscreen.

As the zincating process does not plate any zinc onto the stainlesssteel screen, it is apparent that at this stage the screen is uncoveredwhile the aluminum frame is covered with a layer of zinc.

The final step to rigidize the screen requires plating nickel onto theflexible but taut screen to encapsulate the screen to thereby produce arigid screen. In order to properly plate the nickel it is preferred touse a nickel sulfamate bath with a PH of approximately 5. The higher PHis desirable and preferred as it does not readily attach the zinc layeron the aluminum frame. Furthermore, with a higher PH the nickel forms aharder and stronger deposit around the stainless steel wires whichproduces a substantially stronger screen.

While my process is described with respect to aluminum frames, it isapparent that my process will work equally well with aluminum alloyframes and other active metal frames such as magnesium.

With my process it has also been found that the thickness of the nickellayer need only be on the order of 0.1 mil to 0.2 mil to produce arigidized screen.

I claim:

I. A rigidized self-supporting printing screen comprising:

an aluminum frame for supporting a printing screen,

a layer of zinc encapsulating said aluminum frame to provide aprotective coating around said aluminum frame, a flexible stainlesssteel printing screen stretched tautly across the zinc covered aluminumframe, said flexible printing screen and said zinc covered aluminumframe having a layer of nickel thereon, said layer of nickel on saidflexible printing screen encapsulating said screen to thereby rigidizesaid screen, said layer of encapsulating nickel having a thickness onthe order of 0.1 mil to 0.2 mils to thereby produce a rigidized printingscreen.

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